These beadlike galls are particularly striking because they appear on both surfaces of the leaves. They are small, hemispherical, of variable size and are scattered singly or crowded alongside the midrib. The galls are firmly attached, with the exit holes on the underside. They are shiny externally and the interior contains fleshy tissue. They range from green to yellowish, to red, to reddish brown as they mature. A single leaf may carry numerous galls so that it becomes distorted and its growth inhibited. Although P. laevis is a common species on alder, little is known of its seasonal history and habits. Specimens were abundant in August. The hosts are Oregon or red alder, white alder, and mountain alder in California and hazel alder in Ohio and Georgia.

- Hartford Keifer,Edward Baker,Tokuwo Kono,Mercedes Delfinado,William Styer: (1982) An Illustrated Guide to Plant Abnormalities Caused by Eriophyid Mites in North America^©